Adaptive subsurface not spherical
The problem is that you're using a one-dimensional "Fac" output from the noise texture to produce a scalar displacement.  This is interpreted as a multiple of the vector (1,1,1) and so displaces the cube along the diagonal.  Take the "Color" output of the noise texture to get a three-dimensional noise from (0,0,0) to (1,1,1) and use some Vector Math nodes to center and scale it, like so:



Alternatively, you could take your one dimensional noise and pass it to the "Height" input of a "Displacement" node to get a proper displacement output: